Radio telegraph receiver



Oct. 4, 1955 A. H. DE VOOGT 2,719,913

RADIO TELEGRAPH RECEIVER Filed Jan. 7, 1953 3 Sheets-Sheet 1 TO FIG. lb

IN VEN TOR.

ANT HONE T HUGO DE 1 0067 T0 FIG 10! fi I PRINTER Oct. 4, 1955 A. H. DE VOOGT 2,719,913

RADIO TELEGRAPH RECEIVER Filed Jan. 7, 1955 I 5 Sheets-Sheet 2 INVENTOR. ANTHONE7' IZQGU DE l OOGT ATTY Oct. 4, 1955 A. H. DE VOOGT 2,719,913

RADIO TELEGRAPH RECEIVER Filed Jan. 7, 1953 3 Sheets-Sheet 3 H m m Fig.2

illumll im ul I" INVENTOR. ANTHO/VE T HUGO D5 VOOGT ATT'Y United States Patent RADIO TELEGRAPH RECEIVER Anthonet Hugo de Voogt, The Hague, Netherlands, assignor to Staatshedrijf der Posterijen, Telegrafie en Telefonie, The Hague, Netherlands Application January '7, 1953, Serial No. 330,022

11 Claims. (Cl. 2508) This invention relates to a radio telegraph receiver system. More particularly, it deals with such a receiver for detecting circularly polarized electromagnetic Waves, such as short directional waves, on which binary code signals, such as marks and spaces, are modulated according to right and left, or left and right, rotation of the polarized wave.

Some known systems for transmitting and/ or receiving left and right rotated circular polarized radio wave signals are described in Hammond, In, U. S. Patent 2,272,839, in French Patent No. 660,670 and in an article starting on page 72 of the May, 1949 Tijdschrift van het Nederlands Radio Genootschap (Journal of the Netherlands Radio Society). This journal article points out that ground reflexion horizontally polarizes such radio waves producing a disturbing influence on such systems.

It is an object of this invention to produce a simple, eflicient, effective and economic receiver for left and right rotated circularly polarized directional radio waves, which receiver is unresponsive to false and interfering radio signals.

Another object is to produce such a receiver which is shielded from ground reflected waves that might deform the polarization of the purely circularly or slightly elliptically polarized waves to be detected.

Another object is to produce such a receiver with directional selectivity and which may be adjusted to respond only to purely circularly or slightly elliptically polarized radio waves.

Another object is to produce such a radio receiver which may be adjusted to respond to circularly polarized waves of different intensities, amplitudes and distortions depending upon the receiving conditions.

Another object is to produce such a receiver in which a binary code comprising successive and/or alternate marking and spacing elements may be received and separately detected on a single wave length or radio frequency.

Another object is to produce such a receiver which may be adjusted to respond only to marks, or only to spaces if one or the other signal element becomes subject to some type of persistent mutilation.

Another object is to produce such a circularly polarized wave receiver which is non-responsive to linearly transmitted signals or to wrong direction signals which could operate both the separate mark and space detecting circuits simultaneously.

Generally speaking, the system of this invention comprises two pairs of directional antennae with separate detecting circuits for each pair; one pair of which is employed for receiving and reproducing the circularly polarized wave signals and the other pair of which is employed for discriminating or separating the right-hand rotated from the left-hand rotated portions of the circularly polarized wave, corresponding to the mark and space elements, or vice versa. In order to reduce the interference due to ground reflected waves, both pairs of antennae may be placed behind grounded screens which shield or filter 2,7 19,9 13 Patented Oct. 4, 1955 "ice ' so that the advance and lag, due to right and left rotation of the circularly polarized wave, respectively, when being detected both horizontally and vertically in separate antennae, can produce additive and cancelling effects in the push-pull circuits to positively respond to only one direction of rotation of the wave at a time.

The separate detecting circuits of the receiver are con-.

nected to a pair of cathode ray tubes, each provided with a vertical and horizontal pair of deflection plates, a control grid, and a fluorescent or luminescent screen. The detected circularly polarized wave from the one pair of antennae is connected to the vertical and horizontal reflection plates of each cathode ray tube to produce a closed or elliptical, and preferably purely circular, illuminated trace or pattern on the screen of each of the tubes. The control grids of the separate tubes are connected to the other or discriminating detecting circuit, so that the clockwise or right-hand rotated circularly polarized wave controls one of the tubes, and the counterclockwise or left-hand rotated polarized wave controls the other tube.

Responsive to the illumination on the screen of each tube are separate photoelectric devices, such as photoelectric cells and D. C. amplifiers, which may be regulated to respond to at least a given amount of illumination on the respective screens of the tubes. Between the photoelectric devices and the screens of each tube, is provided a circular mask which may be varied in size and may comprise a disk or an annular aperture, so that only patterns of a given size and substantially circular shape may be responded to by the photoelectric devices. Thus, disturbing elements from the same or other transmitters of the same frequency, which may be detected are masked out by the receiver of this invention, because such false signals distort the closed luminous trace or pattern on the screens of the cathode ray tubes by making it more elliptical so that less light than the required minimum amount will pass the masks to the photoelectric cells and the photoelectric cells will not respond. The outputs of the photoelectric devices may be directly connected to a telegraph printer or other apparatus for recording or converting the marks and spaces received by it into an intelligible message.

The above mentioned and other features and objects of this invention and the manner of attaining them are given more specific disclosure in the following description of an embodiment of this invention taken in conjunction With the accompanying drawings, wherein:

Fig. la is a schematic block and Wiring diagram of the part of the receiver circuit of this invention which detects and separates or discriminates the right rotating from the left rotating circularly polarized radio wave portions, showing the location and shielding for the directional antennae:

Fig. 1b is the other part of the receiver circuit of this invention for reproducing the signals, showing its connection to the other pair of shielded directional antennae, the pair of cathode ray tubes and their corresponding photoelectric devices;

Figs. 2a and 2b are schematic views of two elliptical signal patterns as taken along line II-II of Fig. lb, which patterns are substantially masked and are therefore of false or mutilated signals which will not be re sponded to by the photoelectric devices;

Figs. 2c and 2d are similar to Figs 2a and 2b, but show signal patterns which are not substantially masked and to which photoelectric devices will respond; and

Fig. 2c is an enlarged front elevation of the mask and stand taken alongline, IL-I-I in Fig. lb.

I. The antennae Referring to the left halves of Figs. la and. 1b, there are shown two pairs of' directional antennae, 1314 and 17I8, respectively, each pair being located behind a vertical shielding screen I and 19', respectively. The perspective showing of these antennae and their screens is to illustrate how the circularly polarized electromagnetic wave, which is received from a transmitter radiating.

said Wave in the direction of the arrows 2' and 20, must pass over the top of the screens 1 and 19' in order to induce energy into the antennae 1314' and 171'8. The waves, indicated by the arrows 2" and 20", which strike the ground in front of thescreen are absorbed by the screens 1 and 19, in that ground reflected waves are generally always vertically polarized. If such vertically polarized waves were added to the components of waves 2 or 20, they would materially distort their original purely circular or slightly elliptical polarization. Therefore, in a system of this type wherein the right or left hand rotation of a circularly polarized wave is the modulation of the signal which must be detected by the receiver in as pure a circular form as possible, it is important that as much interference as possible be eliminated from reception by the antennae 1314 and 1718.

These antennae 13-14 and 1718 are shown herein to be loop antennae, although other directional type of antennae may be employed, in which the difference between right and left rotating circularly polarized waves may be separately detected. Since one of the two detecting circuits corresponding to one pair of antennae is required to detect and discriminate or separate the two different types of rotation of the circularly polarized wave, one pair of the loop antennae 13'14 in Fig. 1a, is shown located at right angles to each other and spaced one behind the other at a distance of one quarter of a wave length 4 A) of the frequency of the signal to be received. This is because a circular polarized wave has its horizontal component 90 out of phase with its vertical component, so that when being rotated in the right-hand direction the vertical component has a 90 phase lag behind its horizontal component; and when being rotated in the left-hand direction,v its vertical component has a 90 phase advance with respect to its horizontal component. quency of the wave. polarized wave, the spacing of the antennae 1314 aid in discriminating the right and left rotating waves by transforming them into differences in phase.

Thev other two loop antennae 1718 shown in Fig. 1b

need not be spaced as those shown in Fig. la in that they are employed to detect the intensity of the horizontal and,

vertical component of the signal Wave, and not particularly to. detect which portion of the wave is rotated in.

one direction ad which is rotated in the other direction. However, a similar spacing of antennae as shown in Fig. in may also be employed in Fig. 112, if desired.

II. T he discriminating circuits provided an additional length of conductors shown as loops 3 and 4, respectively, so that the travelling time for the short radio waves. received on the two spaced antennae 13 and 14 will be exactly the same toeach of Thus the cycle of rotation is equal to the fre-- With this property of the circularly the triodes 5, 6, 7 or 8. In the conductors to the triodes 5 and 8 from antenna 14, there are respectively inserted phase shifting devices 9 and 10 for delaying the energy waves to one triode of each push-pull arrangement one quarter of a wave length, or in phase. This delay coupled with the delay of 90 in phase due to the one quarter wave length space between the loop antennae 13i4, produces at the triode 5 with respect to that at the triode 7, energy waves which are out of phase; so that the direct connection between the triode 7 and the antenna 13' will be 180 in advance of the wave energy applied to the triode 5, at all times. Between the plate outputs of the triodes 5 and 7 is connected one coil of a balance transformer T1, the other coil of which is connected to a detector circuit 15 from which a positive D. C. voltage may be withdrawn at the terminal 11, when only one of the triodes 5 or 7 is conductive and the other is cut-01f, as is the case when the potentials applied to their grids are 180 out of phase. Thus, when a circularly polarized wave having a right-hand rotation, say for example corresponding to a marking element in the telegraph system, is received by the antennae 13-14, the energy induced in antenna 13 is at its maximum at the same instant the maximum energy from the wave is induced in antenna 14 (because of the lag of the vertical component of the Wave of 90 behind the horizontal component). Then because of the delay of 90 in the loop 3 and the delay of'another 90 in the phase shifter 9, the triode 5 is non-conductive when the triode 7 is conductive, and vice versa, so that an additive effect is produced in the transformer T1 and energy will be transmitted to form a positive voltage from the terminal 11 indicating that a mark signal element is being received.

The other pair of triodes 6 and 8 are connected respectively to the loop antennae 1.4 and 13, in such a manner that the delay in the distance between the antenna 13 and antenna 14 is counteracted by a delaying device or a 90 phase shifter 10, in the conductor from the antenna 13 to the triode 8. Thus according to the above example for a mark signal, the inputs to these two triodes 6 and 8 will be equal at the same time, as a result of which their respective eifects are cancelled in the balance transformer T2 to which they both are connected. The detector circuit 16 connected to the balance transformer T2 thereby produces no positive voltage output at its terminal 12 when terminal 11 is positive. Therefore, the arrangement P2 is connected to respond to the opposite rotation of the received wave 2 or 20 on antennae 1'314, i. e. a circularly polarized wave which is rotated in the left-hand direction so that the 180 out of phase condition will occur only when the vertical component of the wave is 90 in advance of its horizontal component. Then the inputs of these triodes 6 and 8 will be 180 out of phase and a positive pulse will occur at the output terminal 12 indicating that a space signal element is being received.

Accordingly, when a mark pulse or a right-hand rota tion of the circularly polarized wave is received on the antennae1'314, the triodes 5 and 7 will alternately be conductive so that their outputs will be added in the balanced transformer T1 to produce a positive potential at the terminal; 11 and. the outputs of the triodes 6 and 8 will be equal and simultaneous and therefore will cancel each other in the balance transformer T2 so that no positive potential will be obtained from the terminal 12. Then similarly, when an electromagnetic wave 2 or 20 which is. circularly polarized with left-hand rotation is received on the antennae 131-4, the triodes 5 and 7 will be in phase with each other so their outputs will be cancelled in the balance transformer T1 and no positive potential will be obtained from the terminal 11; and the output of the triodes 6 and 8 will be 180 out of phase so their outputs will be added in the balance transformer T2 and produce a positive potential at the terminal 12. Thus, depending upon which way the received circularly polarized wave is rotated, right or left in response to marks or spaces, correspondingly positive potentials will be obtained from the terminals 11 and 12.

If desired, instead of the phase shifting devices 9 and 10, additional lengths of the conductor may be employed similar to loops 3 and 4, or the loops 3 and 4 may be replaced by phase shifting devices similar to devices 9 and 10, without departing from the scope of this invention.

III. The signal production circuits Referring now to Fig. 1b the signal production part of the receiver is schematically disclosed including a pair of cathode ray tubes 21 and 22, one for each type signal, for example tube 21 for marks and tube 22 for spaces. The energy in the circularly polarized wave 20 or 2 is received in both of the horizontal and vertical loop antennae 17 and 18, each of which is connected to a'radio amplifier 25 and 26, respectively. The outputs of these amplifiers 25 and 26, respectively, are connected to both horizontal pairs and both vertical pair of deflection plates in the cathode ray tubes 21 and 22. Thus, if a purely circularly polarized wave 20 is received, its connection to the cathode ray tubes 21 and 22 will produce a true circular luminous trace or pattern on the fluorescent screens S1 and S2 of both the tubes, but if the wave 20 is not purely circular, i. e. its horizontal and vertical components are unequal, then an elliptical trace or pattern will be produced on both of the screens.

The cathode ray tubes 21 and 22 are connected so that no beam will be formed unless a positive voltage is applied to their grids 31 and 32 (or Wehnelt cylinders). Accordingly, the outputs 11 and 12 from the two circuits 15 and 16 in Fig. 1a are directly applied to these grids 31 and 32, respectively, so that only luminous traces or patterns appear on fluorescent screens S1 and S2 when positive potentials occur at the outputs 11 and 12 in response to mark and space elements, respectively. Since normally a positive potential at terminal 11, according to the circuit in Fig. .la, does not also at the same time permit a positive potential to be applied to the terminal 12, and vice versa, only one of the two cathode ray tubes 21 and 22 will be operated at a time, and they will only be operated correspondingly and during the reception of mark and space elements detected in the circuit of Fig. 1a.

Referring further to Fig. 1b, there are shown corresponding to each of the cathode ray tubes 21 and 22, separate photoelectric devices D1 and D2, respectively, comprising corresponding photoelectric cells 27 and 28 connected to separate amplifier circuits 33 and 34 which may be connected to outputs 35 and 36 that may be directly connected to a telegraph printer or the like device for recording or indicating the received signal elements. These photoelectric cells 27 and 28 are made responsive to the amount of illumination which occurs on the corresponding screens S1 and S2 due to mark and space signal elements, respectively. However, between each of the photoelectric cells 27 and 28, and their corresponding screens S1 and S2, there are preferably provided similar masks 23 and 24 (see also Fig. 22) of opaque material of circular configuration, preferably only permitting annular rings of light to pass them, which rings correspond geometrically with the normal circular traces or patterns which should be produced on the screens S1 and S2 if the mark and space signal elements are properly and correctly received over a purely circularly or slightly elliptically polarized wave. These masks, however, may have different configurations to conform with the requirements of the shape and size of the signal element to be responded to by the photoelectric cells, such as for example only a disk masking just the center of the screen with the light passing around its edges, instead of limited to an annular slot. Also, if desired, there may be provided light concentrating lenses 29 and 30 to focus the light from the annular rings in the masks 23 and 24, respectively, onto the elec- 6 trodes of these corresponding photoelectric cells 27 and 28.

Examples of the types of luminous traces or patterns which may appear on the screens S1 or S2 of the cathode ray tubes 21 and 22 are shown in Figs. 2a, 2b, 2c and 2d. The heavy dark portions of elliptical traces or patterns which may be viewed through the annular slots in the masks are shown in Figs. 2a and 2b, which portions do not supply sufiicient light to the photoelectric cells to cause response, and accordingly signals which are so distorted and influenced by disturbances that they produce relatively flat ellipses, will not be recorded by the receiver of this invention and will be automatically filtered out or ignored. On the other hand, however, a slight amount of distortion may be tolerated, as shown in Fig. 20, wherein the elliptical pattern formed by a received signal is not so distorted that it will not supply suflicient light through the annular aperture in the mask 23 to operate its corresponding photoelectric cell. The ideal condition, however, is shown in Fig. 2d wherein a completely circular signal is received and all of the light which is produced on the fluorescent screen S1 will pass through the annular slot in the mask 23.

The sensitivity of the system of this invention can readily be regulated by varying the sensitivity of the photoelectric amplifiers 33 and/ or 34 so that they will respond to either a lesser or greater predetermined minimum of light or threshold valve. Also, the sensitivity of the system may be varied by varying the size of the annular slot or opening in the masks, or reducing the mask to a central disk of relatively smaller diameter. Furthermore the amplifier circuits employed anywhere in the receiver may be adjusted and/ or provided with automatic volume control circuits and/ or anti-fading control circuits to adjust and maintain the best shape and intensity possible for the luminous trace or pattern projected on the screens S1 and S2 of cathode ray tubes 21 and 22 upon which the signal elements received are produced.

Because of the extreme sensitivity and selectivity of the receiver system of this invention, it can be used for special purposes, and distinguish between other and false signals which may occur even on the same frequency and even from the same direction. Also, if either the mark signals or the space signals are too mutilated for good reception, the half of the system corresponding to the space signals, or mark signals, respectively, may be employed for receiving substantially the whole signal, in that its on and off operation corresponds respectively to spaces and marks or marks and spaces provided synchronism is maintained between the transmitter and receivers printer. However, the reception of both a mark and a space signal simultaneously could cause a blocking of the printer if it could only receive one signal at a time.

While there is described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of this invention.

What is claimed is:

1. In a receiver system for receiving signals modulated according to clockwise and counterclockwise rotation of a circularly polarized electromagnetic wave, said system having means for detecting said Wave and discriminating the clockwise from the counterclockwise rotated portions thereof, the improvement comprising: a pair of cathode ray tubes each having a fluorescent screen, means for producing a luminous pattern on said screens in response to said circularly polarized wave, means for controlling the operation of one of said tubes in response to said clockwise rotation of said wave, means for controlling the operation of the other of said tubes in response to said counterclockwise rotation of said wave, separate photoelectric means corresponding to each said screen and responsive to a predetermined amount of illumination from its corresponding screen, and masks between each said screens and their corresponding photoelectric means to limit the response of said photoelectric means to patterns of a predetermined configuration.

2. A system according to claim 1 wherein said masks are circular and are related in shape and size to the shape and size of a luminous pattern on said screens corresponding to a circularly polarized wave.

3. A telegraph receiver system according to claim 1 wherein one of the directions of rotation of said wave corresponds to a mark signal modulation and the opposite direction of rotation of said wave corresponds to a space signal modulation.

4. A system according to claim 1 wherein said electromagnetic wave is a directional short radio wave of substantially one given frequency;

5. In a receiver for a" right and left rotated circularly polarized single frequency electromagnetic radio wave having two pairs of directional antennae first means coupled to one pair of said antennae for separating the right rotated portions from the left rotated portions of said wave, and second means coupled to the other pair of antennae for detecting both rotations of said wave, the improvement comprising: a pair of cathode ray tubes each having a fluorescent screen, means for applying the detected wave from said second means to both said cathode ray tubes to produce luminous patterns on said screens, means for applying said right rotated wave to control one of said cathode ray tubes, means for applying said left rotated wave to control the other of said cathode ray tubes, separate photoelectric means responsive to the'iilumination on each said screen, and slotted masks between each said screen and its corresponding photoelectric means, whereby only predetermined. luminous patterns on said screens can be responded to by said photoelectric means and detected false patterns will be ignored.

6. A receiver according to claim 5 wherein said antennae comprise loop antennae and one pair of said loop antennae are spaced a quarter wave length of said wave apart in the direction. of the propagation of said wave.

7. A receiver according to claim 5 wherein each of said cathode ray tubes has a control grid and a pair of horizontal and vertical deflection plates; and said means for applying the detected wave from said second means is applied to said deflection plates of both said tubes.

8. A receiver according to claim 7 wherein said means for applying said right rotated wave is connected to the control grid of said one cathode ray tube, and said means for applying said left rotated wave is connected to the control grid of said other cathode ray tube.

9. A receiver according to claim 5 wherein said first means for separating said portions of said wave comprise a pair of push-pull amplifier circuits.

10. A receiver according to claim 5 including grounded shielding means at right angles to the direction of propagation of said Wave and spaced in front of said antennae, whereby ground reflected waves are prevented from affecting said directional antennae.

11. A selective short wave telegraph receiver for receiving and demodulating mark and space signals from a single frequency circularly polarized short radio wave on which the mark signals rotate the plane of polarization in one direction and the space signals rotate the plane of polarization in the opposite direction, said receiver comprising: two pairs of loop antennae with the antennae of each pair being placed at right angles to each other, a grounded screen placed at right angles to and spaced in front of said loop antennae; two separate detector circuits, one being connected to one pair of loop antennae and the other being connected to the other pair of loop antennae; one detector circuit comprising a pair of cathode ray tubes, each tube having a fluorescent screen, two pairs of deflector plates at right angles to each other, and a control grid, said one and corresponding pair of loop antennae being connected to corresponding pairs of said deflector plates to produce at least an elliptical luminous trace on said screens; the other detector circuit comprising separate means responsive to each different direction of rotation of said wave, means for connecting said separate means to separate of said grids of said one detector circuit to control the operation of said cathode ray tubes, one tube for mark signals and the other tube for space signals; separate photoelectric means corresponding to each said screen and responsive to theluminous traces on said screens; and masks with annular slots located between said screens and said photoelectric means to prevent operation of said photoelectric means in response to disturbances which do not produce substantially circular traces on said screens corresponding to said slots.

References Cited in the file of this patent UNITED STATES PATENTS 2,350,331 Salinger June 6, 1944 2,502,394 Smith Mar. 28, 1950' 2,532,428 Smith Dec. 5", 1950 

